1. Field of the Invention
The present invention relates to a position detecting device in which an electrostatic capacity type detection section and an electromagnetic induction type detection section are superimposed on each other, so that a position indicated by either a position indicator or a human body part (e.g., a finger) can be detected.
2. Description of the Related Art
Conventionally, a position detecting device has been used as a device for performing position input in an information-processing device such as a personal computer. In such a position detecting device, a pointing operation or a handwriting input operation such as handwriting a character or hand-drawing an illustration is performed with an input tool such as a pen-like position indicator or a human body part (e.g., a finger).
Input operation using the position indicator as the input tool is performed based on, for example, an electromagnetic resonance technology, in which the position indicator is provided with a resonant circuit that resonates with an electromagnetic wave of a specified frequency transmitted from the position detecting device. Further, a resonance signal induced in the resonant circuit is transmitted to the position detecting device, so that the position indicator indicates its own position to the position detecting device (see, for example, Japanese Unexamined Patent Application Publication No. 7-302153).
Further, input operation using parts of the human body as the input tool is performed based on, for example, an electrostatic capacity technology shown in FIG. 12. FIG. 12 is a view schematically showing an electrostatic capacity type detection section 200. The detection section 200 includes a flat plate-shaped detection electrode 201 and a capacitance measuring circuit 202. When the human body part approaches or contacts with the detection electrode 201, a capacitance is generated between the human body part and the detection electrode 201. The position that the human body part approaches or contacts with is detected as the position of the detection electrode 201 whose capacitance changes due to the change of the capacitance between the human body part and the detection electrode 201. The higher the capacitance between the human body part and the detection electrode 201, the easier the capacitance can be detected. Thus, a flat electrode having an area at or above a predetermined size is used as the detection electrode 201.
In general, since the electromagnetic induction type detection section has high position detecting accuracy compared to the electrostatic capacity type detection section, the electromagnetic induction type detection section is used in a computer, for example, for performing fine input operation such as handwriting a character or hand-drawing an illustration. In contrast, although the electrostatic capacity type detection section has low position detecting accuracy compared to the electromagnetic induction type detection section, it can detect an input operation performed by the human body part. Therefore, an electrostatic capacity type detection section is used in a device such as an automated teller machine (ATM), a cell-phone or the like, in which input operation is performed by directly touching a screen of the device. A newer type of position detecting device has been proposed in which both the electromagnetic induction type detection section and the electrostatic capacity type detection section are effectively utilized.